1. Field of the Invention
The present invention relates to a conductive paste and a laminated ceramic electronic component. In particular, the present invention relates to a conductive paste used with advantage as an internal electrode of a laminated ceramic electronic component, and relates to a monolithic ceramic capacitor.
2. Description of the Related Art
Hitherto, laminated ceramic electronic components, such as monolithic ceramic capacitors, have been provided with a laminate including a plurality of laminated ceramic layers and at least one internal electrode formed along a specified interface between the aforementioned ceramic layers.
In such a laminated ceramic electronic component, in general, the internal electrode is formed by printing and baking a conductive paste in which a conductive powder and an organic vehicle are dispersed in a solvent. More specifically, when the laminated ceramic electronic component is manufactured, a specified ceramic green sheet, which becomes a ceramic layer by baking, is printed with the conductive paste, which becomes an internal electrode, so as to form an electrode coating. Thereafter, a plurality of the aforementioned green sheets are laminated, are press-adhered, and are baked, so that the sintering of the internal electrodes is completed concurrently with the completion of sintering of the ceramic layers, and a ceramic laminate provided with the internal electrodes is formed. At this time, the melting point of the conductive powder constituting the internal electrodes must be higher than the sintering temperature of the ceramic. When the melting point of the conductive powder is lower than the sintering temperature of the ceramic, the conductive powder is molten during the baking, so that a break or crack is generated in the internal electrode after the baking so as to reduce coverage. Therefore, as the conductive powder constituting the internal electrode, Pt, Pd, W, Nb, Ni, etc., can be selected, and in addition to this, in order to realize reduction of the cost, a base metal, e.g., Ni, is used as the conductive powder.
In the laminated ceramic electronic component using such a base metal such as Ni for the internal electrode, however, accompanying the decrease in the layer thickness and the increase in the number of layers of the ceramic layers, a large residual stress is generated at the interface between the internal electrode and the ceramic layer due to the difference of shrinkages and the difference of coefficients of thermal expansion between the electrode coating formed by printing and the green ceramic layer during the baking. As a consequence, there is a problem in that the thermal shock resistance of the laminated ceramic electronic component is degraded. Furthermore, there is a problem in that the reliability at a high temperature and high humidity, that is, the moisture load resistance characteristics, is also degraded accompanying the decrease in the layer thickness and the increase in the number of layers of the ceramic layers.
Accompanying the decrease in the thickness of each ceramic layer, the thickness of the internal electrode must be decreased. Accordingly, the particle diameter of the conductive powder in the conductive paste for constituting the internal electrode must be further decreased. When the particle diameter of the conductive powder is further decreased, since the shrinkage of the internal electrode due to the sintering of the conductive powder occurs at a lower temperature during the baking, there is a problem in that delamination is likely to occur.
In order to solve the latter problem, for example, in Japanese Examined Patent Application Publication No. 7-56850, a monolithic ceramic capacitor in which a Ni internal electrode and a ceramic layer are connected with an aluminosilicate layer is disclosed. Regarding this monolithic ceramic capacitor, however, an improvement of the aforementioned problem, that is, the improvement of the thermal shock resistance, is not intended.
Furthermore, in Japanese Unexamined Patent Application Publication No. 8-259847, a conductive paste using a metallic powder coated with a reaction product of an organic silicon compound and water is disclosed. When this conductive paste is used for an internal electrode of a monolithic ceramic capacitor, however, since abnormal particle growth of the ceramic occurs due to a reaction of silicon in the paste and the ceramic, this is not effective to improve the aforementioned problem, that is, to improve the thermal shock resistance.
Accordingly, it is an object of the present invention to provide a conductive paste in which the delamination does not occur during a step of baking, having superior thermal shock resistance and superior moisture load resistance characteristics. It is another object to provide a laminated ceramic electronic component in which an internal electrode is formed using the aforementioned conductive paste.
In order to achieve the aforementioned objects, a conductive paste according to an aspect of the present invention is composed of a conductive powder primarily containing Ni, an organic vehicle, and a compound A containing at least one of Mg and Ca and at least one material selected from the group consisting of an organic acid metal salt, an oxide powder, a metal organic complex salt and an alkoxide, in which a compound B having a hydrolyzable reactive group containing at least one of Ti and Zr adheres to the surface of the aforementioned conductive powder.
A conductive paste according to another aspect of the present invention is composed of a conductive powder primarily containing Ni and an organic vehicle in which a compound A and a compound B adhere to the surface of the aforementioned conductive powder, the compound A contains at least one of Mg and Ca and is at least one organic acid metal salt, oxide powder, metal organic complex salt and/or alkoxide, and the compound B has a reactive group containing at least one of Ti and Zr.
The reactive group of the aforementioned compound B is preferably an alkoxyl group.
The aforementioned compound B is preferably an alkoxide.
The aforementioned compound B is preferably a coupling agent.
The adhesion amount of the aforementioned compound B is preferably about 0.1% to 5.0% by weight in terms of TiO2 and ZrO2 relative to 100% by weight of the aforementioned conductive powder.
The mole ratio of the total amount of Ti and Zr, in terms of TiO2 and ZrO2 contained in the aforementioned compound B, relative to the total amount of Mg and Ca, in terms of MgO and CaO contained in the aforementioned compound A, is preferably about 0.5 to 4.0.
A laminated ceramic electronic component according to another aspect of the present invention is provided with a ceramic laminate including a plurality of laminated ceramic layers and an internal electrode formed along an interface between the aforementioned ceramic layers in which the aforementioned internal electrode is formed by baking the aforementioned conductive paste according to the present invention.
The laminated ceramic electronic component according to the present invention is preferably further provided with a plurality of terminal electrodes provided at different positions on the end faces of the aforementioned laminate, and in which a plurality of aforementioned internal electrodes are electrically connected to one of the terminal electrodes.
The aforementioned ceramic layer in the laminated ceramic electronic component according to the present invention may be composed of a dielectric ceramic primarily containing barium titanate.